The present embodiments relate to a radiation diaphragm for an x-ray facility and an x-ray facility with such a radiation diaphragm.
Radiation diaphragms are used in x-ray facilities to narrow an x-ray beam produced by an x-ray tube to form a useful beam. Regions outside the useful beam are masked out by the radiation diaphragm, so that the radiation diaphragm's form decides the residual contour of the useful beam. It is expedient to vary the contour as a function of the respective task. When examining patients or bodies, the aim is to achieve a contour of the useful beam that is tailored to the volume to be examined, to avoid exposing the surrounding region to an unnecessary radiation dose.
Radiation diaphragms disposed in the immediate proximity of the x-ray tube are also referred to as primary radiation diaphragms. Primary radiation diaphragms frequently have a number of individual diaphragms, disposed at different distances from the x-ray tube. The x-ray beam is initially roughly narrowed by a diaphragm disposed first in the beam path, sometimes referred to as a collimator, which brings about an approximately rectangular definition of the beam by one or two pairs of diaphragm plates. Finer definition of the beam path, the contour of which is not necessarily set as rectangular in form, then takes place by a similarly adjustable diaphragm disposed in the beam path.
EP 0 485 742 discloses a further diaphragm that can be embodied as an iris diaphragm. Generally, iris diaphragms produce an approximately circular definition of the x-ray beam. The diameter or typical size of the x-ray beam can be adjusted extremely finely, usually in a continuous manner. Iris diaphragms have a relatively large number of moving parts. Iris diaphragms are complex to construct and expensive to produce. Iris diaphragms have louvers, which are mounted in a displaceable manner and bring about the actual masking of regions of the x-ray beam that are not of interest. The louvers themselves and also their mounting are susceptible to damage due to the louver movement.
BE 100 9333 discloses a radiation diaphragm for a portable x-ray facility. The radiation diaphragm is designed as a perforated diaphragm. The radiation diaphragm has a radiation defining device, formed as a cylinder and disposed concentrically in relation to the x-ray tube. The radiation diaphragm has a plurality of diaphragm apertures, each being able to be positioned by rotating the radiation defining means in front of the beam emission window. The cylindrical form of the radiation defining means has to be tailored to the x-ray tube, around which it is disposed. The radiation defining means cannot be disposed freely but requires an arrangement that is concentric to the x-ray tube. This arrangement requires a complex rotational mounting, since the x-ray tube is disposed in the center of the radiation defining means, where a rotation axis should advantageously be disposed.